Electron-beam-processing machine having means for deflecting impurities from the path of the electron beam

ABSTRACT

Apparatus in electron-beam-processing machines for keeping the path of the working beam free of impurities, the apparatus having a screening device associated with the working beam for catching impurities, comprising an ionization device acting in the region of the working beam path, and a deflecting device effective in the region of the said beam path to produce a deflecting field for electrically charged particles, the ionization device being so formed that it acts with an ionization probability greater than that of the working beam on atom-sized or larger particles, the deflecting device exerting a sufficient deflecting action on such electrically charged particles, which move at substantially thermal speeds as to remove these particles from the path of the working beam.

United States Patent ELECTRON-BEAM-PROCESSING MACHINE HAVING MEANS FORDEFLECTING IMPURITIES FROM THE PATH OF THE ELECTRON BEAM 29 Claims, 10Drawing Figs.

U.S. Cl ..219/121EB, 13/31, 250/495 R, 313/7 Int. Cl ..B23kl5/00, H01j37/26 Field of Search 13/31; 219/121 EB; 250/495 R, 49.5 TE, 49.5 A,49.5 C,

49.5 D, 49.5 PE; 313/7; 417/48, 49

[56] References Cited UNITED STATES PATENTS 3,005,859 10/1961 Candidus13/31 3,156,811 11/1964 Barry 219/121 EB Primary Examiner-James W.Lawrence Assistant Examiner-A. L. Birch Arlomey- Kenyon & Kenyon ReillyCarr & Chapin ABSTRACT: Apparatus in electron-beam-processing machinesfor keeping the path of the working beam free of impurities, theapparatus having a screening device associated with the working beam forcatching impurities, comprising an ionization device acting in theregion of the working beam path, and a deflecting device effective inthe region of the said beam path to produce a deflecting field forelectrically charged particles, the ionization device being so formedthat it acts with an ionization probability greater than that of theworking beam on atom-sized or larger particles, the deflecting deviceexerting a sufficient deflecting action on such electrically chargedparticles, which move at substantially thermal speeds as to remove theseparticles from the path of the working beam.

PATENTEDNUV 23 Ian SHEET 1 OF 3 4 irWIMIII/III.

PATENTEbunv 23 nan sum 3 of 3 Fig.7

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INVI'IN'I'ORI Kmtu f/swz STE/G Ru/A D ELECTRON-BEAM-PROCESSING MACHINEHAVING MEANS FOR DEFLECTING IMPURITIES FROM THE 1 PATH OF THE ELECTRONBEAM PRIOR APPLICATION When processing workpieces withelectron-beamprocessing machines, the material at the beam impact pointis caused to evaporate or scatter; but this material appears as animpurity in the machine and can cause high-tension flashovers at thebeam source. Screening devices usually associated with the working beamare unable to present such impurities from v flying directly into .thebeam path.

To avoid such interference, it has been proposed to direct theenergybeam through screens axially offset relative to one another by adeflecting device. The beam has deflected errors impressed thereon whichhave to be compensated to prevent them fromthe causing the properties ofthe working spot to deteriorate. Other means for avoiding the .saidinterference use prismatic accelarators'ec tions, e.g. electrostaticfields with a curved oi tilted axis of rotation, or rotationallysymmetrical electrostatic lenses which are intended to filter out thedisturbing stream of impuritiesfrom the beam. Even these means havedisadvantages. With prismatic accelerator fields the cathode is indeedprotected, but it does not prevent particles from entering theaccelerating sections. Electrostatic lens arrangements only act oncharged particles, and since the degree of ionization owing to the veryhigh electron speed in electron beam processing machines is very low,the majority of neutral, particles are not filtered out.

The object of the present invention is to protect the beam source fromthe action of impurities by simple means, and 'in a highly effectivemanner.

According to the present invention there is provided an apparatus inelectron-beam-processing machine for keeping the path of the workingbeam free of impurities, the apparatus having a screening deviceassociated with the working beam for catching impurities, comprising anionization device acting in the region of the working beam path, and adeflecting device effective in the region of the said beam path toproduce a deflecting field for electrically charged particles, theionization device bring so formed that it acts with an ionization devicegreater than that of the working beam on atom-sized or larger particles.the deflecting device exerting a sufficient deflecting action on suchelectrically charged particles, which inove at substantially thermalspeeds as to remove these particles from the path of the working beam.

In the apparatus of the invention, the use of an ionizing deviceproducing a high degree of ionization ensures that a large proportion ofthe uncharged particles of impurity is ionized. These ionized particles,owing to their relatively low (substantially thermal) speeds, can beeffectively deflected from the beam path of the working beam, and heldback by the screening devices by relatively week deflecting means, whichhave no noticeable deflecting effect on the relatively fast electrons.

The ionization may be carried out in a variety of ways, as for example,by ionizing beams such as ultraviolet radiation, slow electrons or thelike. The deflecting device may include electrostatic, electromagneticor magnetostatic units. Tests with conventional electron beamsprocessing machines with beam outputs of between i and I kw. have shownthat ionization devices which operate with slow electrons can be used inpath of the working beam over a distance of IO cm. with a currentdensity of lamp per cm. whereby this giving a decisive improvement inthe separating effect relative to arrangements without additionalionization. Furthermore it has been found that U l=0volts andU2+l00volts.

that when using electrostatic deflecting devices, very low deflectingvoltages of a few hundred volts can be used; with such low deflectingvoltages electrons of the working beam, which have energies in the orderof magnitude of 0.1 mev. are only insignificantly deflected, and theproperties of the working beam remain substantially unchanged.

Theinvention will be described with reference to the accompanyingdrawings, In which:

FIG. 1 is a schematic longitudinal section through an electron beammachine with deflecting devices,

FIG. 2 is a schematic longitudinal section similar to FIG. 1 through anelectron-beam-processing machine with a deflecting device in accordancewith the invention,

FIG. 3 is an alternative embodiment of an electron beam machine with adevice in accordance with the invention,

FIG. 4 is a part view of an embodiment of an device in accordance withthe invention, enlarged relative to FIGS. 1 to 3,

FIG. 5 is a section taken at right angles to the working beam of analternative embodiment of a deflecting device in accordance with theinvention,

FIG. 6 is a sectional view of a further embodiment of a device inaccordance with the invention, also taken at right angles to the workingbeam,

FIG. 7 isa fragmentary view of a further embodiment of a device inaccordance with the invention, shown as in axial section with respect tothe beam,

FIG. 8 is a transverse sectional view of a further embodiment,

FIG. 9 is a perspective view of the FIG. 8,

FIG. 10 is an axial section of a further embodiment of a device inaccordance with the invention. The electron beam machine shown in FIG. 1contains essentially a cathode 2, a control electrode 4, an anode 6 anda focusing device 8. The energy beam 10 has a beam axis and is focusedon the processing point 14 of a workpiece to be processed. Processingmay involve milling, boring, cutting, welding, heating, annealing andthe like. During processing, the workpiece 16 produces substances suchas occluded gases evaporated workpiece material, and spattered workpieceparticles at the processing point 14 which constitute undesiredimpurities. These intrude on the path of the electron-beam-processingmachine and especially the acceleration section thereof. To keep thebeam path substantially free of such impurities a screen device isprovided, which in the simplest case is a single screen e.g., the anodescreen 6. Preferably a further screen 18 is mounted over the workpiece.The machine shown also contains a further screen 20 below the focusingdevice 8. The openings of the screens are slightly greater than the beamdiameter at the location of the screens.

The machine shown in FIG. I also contains a deflecting device forionized impurity components; this is in an electrostatic deflectingdevice and consists of two plate-shaped deflecting electrodes 22, 24which are arranged on each side of the beam path and are preferablyreplaceable. The deflecting electrodes may also be of arcuate sectionand curved around the beam. The potentials of the deflecting electrodes22 and 24 are designated by Uland U2. These potentials are smallcompared with the accelerating voltage used to form the working beam 10,this voltage exists between the cathode system 2, 4 and: the anode 6 andmay be in the region of l00kv. The potentials of the deflectingelectrodes may be such With defection potentials of this order, theworking beam 10 consisting of relatively fast electrons is notnoticeably deflected; since, however, the speeds of the particles ofimpurities released at the processing point 14 are relatively low andmainly determined by the temperature prevailing at the processing point,such deflecting voltages suffice to remove ionized particles ofimpurities from the beam path. The particles are deposited either on thedeflecting electrodes themselves, or on the adjacent screens, e.g.screen 20 or the anode screen 6. It is obvious, that with statedpotentials of the deflecting electrodes 22, 24, positive embodimentshown in particles of impurities are deflected to the left in FIG. I,and negative particles of impurities are deflected to the right. In anycase, the deflecting device is so formed that over a part of the path ofthe working beam it produces a deflecting field acting transversely tothe beam path.

To improve the eflect, several deflecting devices may be provided in themachine of FIG. 1. Thus the deflecting device 22, 24 already describedmay be supplemented by a second deflecting device with electrodes 26 and28 located above the focusing device 8. To reduce the effect of thedeflecting devices on the working beam 10, this second deflecting device26, 28 can be operated with a reversed polarity as compared with thefirst deflecting device 22, 24, for example, the deflecting electrode 26may be connected to a potential U,=300 volts and the deflectingelectrode 28 to a potential U O volts. It should be understood that thepotential values given are merely examples and that in practice lowerpotentials, of the order of 100 v. give quite satisfactory deflectingactions especially with working beams of relatively small diameter,where the deflecting electrodes can be located closely together. Thedeflecting electrodes 26, 28 are preferably replaceable; the screen andthe anode screen 6 may also be replaceable. Since the relatively fastelectrons of the working beam 10 exert only a small ionizing effect, anionizing device acting in the region of the path of the working beam 1is provided in the electron beam processing machine shown in FIG. 2 thisis so designed that it acts more strongly on the particles of impuritieslocated in the beam path then the working beam 10. In the embodimentshown in FIG. 2 the first deflecting device comprising the deflectingelectrodes 22 and 24 is provided with a first ionization device 30,which is shown as an ultraviolet radiator 32. The second deflectingdevice which consists of the deflecting electrodes 26 and 28, isprovided with a second ionizing device 34 which is shown as an auxiliaryelectron source 36 with an auxiliary cathode 42 operated via supplyleads 38, 40. The ionizing devices 30 and 34 are each located at theends of the associated deflecting devices 24 or 26,-remote from the beamsource 2, 4, 6. This is because the flight direction of the particles ofimpurities is generally opposite to the direction of movement of theelectrons of the main beam [0, i.e. upwards in FIGS. 1 and 2. In theembodiment of FIG. 2 the ionization devices 32, 34 act through cutouts44, 44 in the deflecting electrodes on the space traversed by theworking beam 10. With reference to the second ionization device 34operating with an auxiliary cathode 42, the auxiliary electrons emittedby the electrode 42 can be accelerated into the deflecting field betweenthe deflecting electrodes 26 and 28. For this purpose the deflectingelectrode 26, through the cutout 44 of which the auxiliary electronsenter the beam path, is operated at a relatively negative potential. Thepotential a of the deflecting electrode may be 26 volts, whilst thepotential u of the deflecting electrode 28 can be +l00 volts. Instead ofthe electrons emitted by the auxiliary source of electrons beingaccelerated in the deflecting field, the auxiliary electron source mayalso have its own accelerating system associated therewith; suchembodiments are described below.

The embodiment shown in FIG. 2 also contains screens 18 and 20; it is ofparticular importance that above and between the individual deflectingdevices screens 20 and 6 are provided. If it is desired to avoidchanging the anode screen 6, this screen 6 may have an interchangeablescreen (not shown) located near it.

In the embodiment shown in FIG. 3 the first ionization device 30 has anauxiliary electron source 46 with an auxiliary cathode 48. The auxiliarycathode is heated via supply leads 50 and 52. A screen 54 is connectedwith the deflecting electrode 24 so as to interfere as little aspossible with the deflecting field' of the lower or first deflectingdevice 22, 24. A further feature of the embodiment shown in FIG. 3 isthat the auxiliary cathode 42 of the second ionization device 34 islocated within the focusing device 8 which as usual is a magnetic coil.As a result, the magnetic focusing device 8 acts with respect to theslower auxiliary electrons emitted by the magnetic focusing device 8 asa magnetic deflector which in known manner extends the tracks of theseauxiliary electrons by curving or spiraling them and accordinglyincreases their ionization probability in the ionization region betweenthe deflecting electrodes 26 and 28. It is, of course, readily possibleto provide a separate magnetic auxiliary device, in order to extend thetracks of the auxiliary electrons by curvature or spiraling. Theembodiment shown in FIG. 4 corresponds substantially to the lower part(first deflecting and ionization device) of FIG. 3, but with thedifference that the auxiliary electron source 46 (with the auxiliaryelectrode 48) of the first ionization device 30 has its own acceleratingsystem associated therewith, this consisting of the auxiliary controlelectrode 56 and auxiliary anode 58. These two electrodes may be sieveor lattice like devices and the auxiliary control electrode 56 may bemade as a slotted screen. The auxiliary control electrode 56, like thescreen 54, is supplied with a potential which is slightly negativerelative to the auxiliary cathode 48, and is preferably regulatable,whilst the auxiliary anode 58 is fed with a potential which is positiverelative to the auxiliary cathode 48, so that the auxiliary electronsemitted from the cathode 48 are accelerated by the anode 58 in quantityand focusing which are controllable by the potential of the auxiliarycontrol electrode 56. These electrons enter the ionization regionthrough meshes the meshes of electrode 56 and through the cutouts 42 ofthe deflecting electrode 24, in the ionization region between thedeflecting electrodes 22 and 24. The figure shows schematically thedeflection of positive and negative particles of impurity to therelatively negative deflecting electrode 24 or the relatively positivedeflecting electrode 22. The direction of flight of the particles ofimpurities is indicated by the arrow 60, and the direction of theworking beam by the arrow 62. The arrows 64 indicate tracks of auxiliaryelectrons. FIG. 4 also shows that the parts of the ionization device aresupported in two insulating material blocks 66, 68, which turn in arefastened to the deflecting electrode 24 by means of screws 70, 72.

FIG. 5 is a section normal to the working beam 10, and shows anauxiliary electron source 74 having an auxiliary cathode 76 providedwith its own focusing device. This focusling device is' formed as anelectrostatic cylinder lens and consists of an auxiliary controlelectrode 78, which is held at a preferably regulatable potential,slightly negative relative to the auxiliary electrode 76, with apositive auxiliary anode relative to the auxiliary cathode 74 and adeflecting electrode 82 negative with respect to the cathode 76. Inthese electrodes slots are formed extending parallel to the auxiliarycathode 76, and on the other side of the working beam 10 there is apositive deflecting electrode 84 substantially parallel to thedeflecting electrode 82 and positive relative to the auxiliary cathode76, so that the auxiliary electrons emitted by the auxillary cathode 76follow tracks indicated by the lines 86. The electrostatic focusingdevice for the auxiliary electrons shown in FIG. 5 with the auxiliarycathode 78 parallel to the working beam, results in a substantiallyline-shaped focusing in the plane of the working beam 10, so thationization probability is correspondingly increased.

FIG. 6 shows a multiple use of the principle shown in FIG 5. Thus,around a part of the circumference of the working beam 10 there areseveral deflecting electrodes 82 of substantially equal potentials, andauxiliary electron sources 74 each including an auxiliary cathode 76 andauxiliary control electrode 78. Over part of the remaining portion ofthe circumference of the beam a relatively positive deflecting electrode84 is provided. It is readily seen that as shown in FIG. 6 theelectrodes 78, and 82 belonging to the individual auxiliary cathodes 76are formed as circumferential sections of cylindrical surfaces, betweenwhich there are corresponding slotlike cutouts for the passage of thelinear by focused auxiliary electron tracks 86. It has been that withthe focusing means of FIG. 6, overlapping of the auxiliary electrontracks 86 and an accordingly high auxiliary electron current density isobtained in the associated axial region of the Working beam 10.

The embodiment shown in FIG. 7 contains an electron source 88 with anannular auxiliary cathode 90 surrounding the working beam 10. There isalso an annular auxiliary anode 92 offset in the direction ofthe beam,which accelerates the auxiliary electrons emitted by the auxiliarycathode 90 substantially parallel to the working beam 10. In thearrangement shown in FIG. 7 there is also an electrostatic focusingdevice with ring electrodes 94 and 96. In operation the electrode 94 mayhave a potential of +l00 v. the electrode 96 a potential of 100 v. andthe anode 92 a potential of +300 v. Furthermore a control-electrode (notshown) may also be provided near the auxiliary cathode 90, to allow theemission current to be adjusted in a manner known in connection withWehnelt electrodes. From the form of the auxiliary electron source theauxiliary electrons are focused along the axis of the working beam andaccordingly there is an increased rate of ionization. The particles ofimpurities ionized in the ionizing region, if they are'not caught by thescreen 20, are deflected from the path of the working beam by deflectingdevice. This deflecting device is offset against the direction of thebeam with respect to the auxiliary electron source 88, i.e. it islocated on the side of the auxiliary electron source 88 remote from theworkpiece to be processed. The direction of the working beam 10 is againindicated by arrow 62 in FIG. 7.

FIG. 7 also'shows the use of an additional magnetic device in the formof a ring magnet 98, to obtain an additional focusing of the auxiliaryelectrons or even, with a correspondingly powerful magnet, an elongationof the auxiliary electron tracks by curving or spiralling. Someauxiliary electron tracks 100, which are obtainable with the arrangementof FIG. 7, are indicated therein; some magnetic lines of force 102 arealso shown.

In the embodiment shown in FIGS. 8 and 9 an auxiliary electron source104 is used having an auxiliary cathode 106 extending substantiallyparallel to the working beam 10. The auxiliary cathode 106 is enclosedby a grid 108, which in the manner usual in electron tubes may consisteither of a wire mesh,- oras shown in FIG. 8, a wire spiral supported onrods 110, 112. The grid 108 and the working beam are enclosed by anenvelope electrode which in FIG. 9 is shown as a wire spiral supportedon two rods 116, 118 but may also consist of a wire mesh, or aperforated or imperforate sheet. In operation, the grid 108 is held at apositive potential relative to the auxiliary cathode 108 and theenvelope electrode 114 at a potential negative relative to the auxiliarycathode 106. By suitable selection of the potential of the lattice 108and the envelope electrode 114 with reference to'the potential of theauxiliary electrode 106, and with suitable spacing of the grid 108 withelectrons emitted by the auxiliary cathode 106 are concentrated in thespace between the grid 108 and the auxiliary electrode 114, so that'therepulsion of the auxiliary electrons at the envelope electrode 114 andthe acceleration of these electrons through the grid 108 result inoscillating auxiliary electron track, thus highly increasing the rate ofionization in the region of the working beam 10. The relatively heavynegative and positive particles produced by ionization of impurities aredeflected to the grid 108 or towards the envelope electrode 114 wherethey are at least partly deposited. It is also possible to provideadditional collecting electrodes (not shown). It is of course alsoexpedient in the embodiment of FIGS. 8 and 9, to cover the cross sectionoutside the working beam 10 by screens in the axial regions outside theionization and deflecting device on which screens the impurities aredeposited.

Suitable data for the operation of the embodiment shown in FIGS. 8 and 9are readily ascertained by tests; this applies both to the potentialsused and to the spacing of the turns of the grid 108 and of the envelopeelectrode 114. It should be particularly noted that in the embodiment ofFIGS. 8 and 9, the grid 108 and the envelope electrode 114 operates asdeflecting devices; is it also possible to provide additional deflectingelectrodes.

When the working beam passes through an intermediate partially evacuatedchamber, deflecting and ionization devices may also be provided in theintermediate chamber or even outside it. Owing to the relatively highgas pressure therein, ionization devices may also be used in whichauxiliary electrons producing the ionization are obtained from a coldcathode, e.g. by peak discharge or from a high current are; again,magnetic auxiliary devices such as the ring magnet 98 shown in FIG. 7may be used, to extend the auxiliary electron tracks by curving orspiralling. An arrangement with a highcurrent arc is shown schematicallyin FIG. 10. In a chamber of an intermediate pressure stage systemlocated over the workpiece 16, not shown in detail, deflectingelectrodes 22, 24 are arranged on both sides .of the path of the workingbeam 10. The ionization device is here formed by the workpiece 16 and anauxiliary electrode 122 located thereover, which has a screen opening124 for the passage of the working beam 10 and an annular projection 126surrounding this opening. Between this projection 126 and the workpiece16 a high-current are 128 is struck and maintained: the very powerfulelectric ionization produced acts to prevent the impurities formed fromflying through the screen opening 124 against the beam direction. Theauxiliary electrode 122 forms the outermost closure wall of theintermediate pressure stage system; in this case a minute opening 124 isused.

Ail embodiments are similar in that the acceleration distance of theworking beam, e.g. in FIGS. 1 to 3 the distance between the cathode 2and the anode 6, lies outside the operative regionof the deflectingdevice. This device and the associated ionization means are thus locatedin a space free of high-tension fields.

Other embodiments are possible, including the provision of more than twodeflecting and ionization devices one after the other, in the directionof the beam.

1 claim:

1. In electron-beam-processing machines apparatus for keeping the pathof the working beam free of impurities, comprising a screening deviceassociated with said working beam for catching impurities, an ionizationdevice acting in the region of the said beam path to produce anionization probability greater than that of said working beam onparticles of impurity therein, and a deflecting device producing adeflecting field for said ionized particles, effective in the region ofsaid working beam to remove said particles from said beam path.

2. Apparatus as recited in claim 1, wherein said deflecting deviceproducesa deflecting field transverse of said beam path along at least aproportion of said path.

3. Apparatus as recited in claim 1 wherein said ionization device isarranged in an end region of said deflecting device remote from thesource of said beam.

4. Apparatus as recited in claim 2 comprising a plurality of deflectingdevices acting over a part of said beam path on said ionized particles.

5. Apparatus as recited in claim 4, comprising at least two deflectingdevices acting on said ionized particles with opposite deflectingactions.

6. Apparatus as recited claim 4, comprisinga plurality of ionizationdevices spread out along said beam path.

7. Apparatus as recited in claim 6, with at least one ionization deviceassociated with each deflecting device.

8. Apparatus as recited in claim 4, comprising a screen betweenindividual adjacent deflecting devices. A

9. Apparatus as recited in claim 1, wherein said deflecting devicecomprises electrostatically acting deflecting electrodes arranged alongsaid beam path, said electrodes having means ensuring easy replacementthereof.

10. Apparatus as recited in claim 1, wherein said ionization devicecomprises an auxiliary electron source, which produces electrons oflower energy than the electrons in said working beam.

11. Apparatus as recited in claim 10, comprising an acceleration systemfor each said auxiliary electron source.

12. Apparatus as recited in claim 10, comprising a focusing device foreach auxiliary electron source, said focusing device producing linearfocusing of electrons from said auxiliary source.

13. Apparatus as recited in claim 1, comprising a glow discharge spacein said ionization device for ionization of said particles ofimpurities.

14. Apparatus as recited in claim 1, comprising a high-current arcdischarge space in said ionization device for ionization of saidparticles of impurities.

15. Apparatus as recited in claim 14, comprising an auxiliary electrodeprovided with a small aperture, said high-current discharge spaceextending between the impact region of the working beam on the workpieceand said auxiliary electrode.

16. Apparatus as recited in claim 10, wherein said auxiliary electronsource is provided with an auxiliary cathode extending parallel to saidworking beam.

17. Apparatus as recited in claim 16, comprising a grid surrounding saidauxiliary cathode and an envelope electrode surrounding said workingbeam and said grid.

18. Apparatus as recited in claim 17 comprising a grid surrounding saidelectron source which is at a positive potential relative thereto and anenvelope electrode surrounding said grid and at a negative potentialrelative to said electron source, said potentials and the spacings ofsaid grid causing electrons emitted by said electron source to beconcentrated in the space between said grid and said envelope electrodeand to execute oscillatory movement therein to produce relatively heavynegative and positive particles by ionization of impurities, saidnegative particles concentrating at said grid and said positiveparticles concentrating at said envelope electrode, said particles beingat least in part, deposited on said grid and said electrode.

19. Apparatus as recited in claim 9, wherein said ionization devicecomprises an auxiliary electron source which produces electrons of lowerenergy than the electrons in said working beam, the apparatus furthercomprising at least two deflecting electrodes provided on opposite sidesof said working beam said electrodes being charged to different electricpotentials, said auxiliary electron source being so positioned thatauxiliary electrons generated thereby to produce ionization areaccelerated in the electric field between said deflecting electrodes.

20. Apparatus as recited in claim 9, wherein said ionization devicecomprises an auxiliary electron source and a negative deflectingelectrode associated therewith, said electrode defining an aperture nearwhich said source is located.

21. Apparatus as recited in claim 19, comprising a plurality ofauxiliary electron sources and deflecting electrodes arranged aroundpart of the circumference of said working beam. said electrodesconnected to substantially the same potential, and at least onerelatively positive deflecting electrode occupying at least part of theremaining circumference.

22. Apparatus as recited in claim 10, wherein said auxiliary electronsource is so formed that the low-energy electrons therefrom move in theregion of said working beam and substantially parallel thereto.

23. Apparatus as recited in claim 22, wherein said auxiliary electronsource is provided with an auxiliary cathode at least partly surroundingthe path of said working beam and an annular auxiliary anode offset withrespect thereto along the direction of said working beam, said auxiliaryanode accelerating the electrons emitted by said auxiliary cathodesubstantially parallel to said working beam.

24. Apparatus as recited in claim 23, comprising at least one deflectingdevice in an axial region of said working beam on the side of saidauxiliary electron source remote from said workpiece to be processed.

25. Apparatus as recited in claim 23, comprising a focusing device forsaid auxiliary electron source, wherein said focusing device is soformed that it concentrates said electrons into a substantiallycylindrical space extending substantially coaxi- .al to said workingbeam.

26. Apparatus as recited in claim 10, comprising a magnetic device whichin the ionization region of said apparatus extends the tracks of saidelectrons supplied by said auxiliary electron device by curvaturethereof.

27. Apparatus as recited in claim 26, comprising a working beam magneticfocusing device. wherein said auxiliary electron source is so arrangedthat said magnetic focusing device also acts to curve the tracks ofelectrons emitted by said ionization device.

28. Apparatus as recited in claim 1, wherein the acceleration path ofthe electrons in said working beam lies outside of the working region ofsaid deflecting device.

29. Apparatus as recited in claim 1, wherein said screening device isprovided with at least one replaceable screen.

1. In electron-beam-processing machines apparatus for keeping the pathof the working beam free of impurities, comprising a screening deviceassociated with said working beam for catching impurities, an ionizationdevice acting in the region of the said beam path to produce anionization probability greater than that of said working beam onparticles of impurity therein, and a deflecting device producing adeflecting field for said ionized particles, effective in the region ofsaid working beam to remove said particles from said beam path. 2.Apparatus as recited in claim 1, wherein said deflecting device producesa deflecting field transverse of said beam path along at least aproportion of said path.
 3. Apparatus as recited in claim 1 wherein saidionization device is arranged in an end region of said deflecting deviceremote from the source of said beam.
 4. Apparatus as recited in claim 2comprising a plurality of deflecting devices acting over a part of saidbeam path on said ionized particles.
 5. Apparatus as recited in claim 4,comprising at least two deflecting devices acting on said ionizedparticles with opposite deflecting actions.
 6. Apparatus as recited inclaim 4, comprising a plurality of ionization devices spread out alongsaid beam path.
 7. Apparatus as recited in claim 6, with at least oneionization device associated with each deflecting device.
 8. Apparatusas recited in claim 4, comprising a screen between individual adjacentdeflecting devices.
 9. Apparatus as recited in claim 1, wherein saiddeflecting device comprises electrostatically acting deflectingelectrodes arranged along said beam path, said electrodes having meansensuring easy replacement thereof.
 10. Apparatus as recited in claim 1,wherein said ionization device comprises an auxiliary electron source,which produces electrons of lower energy than the electrons in saidworking beam.
 11. Apparatus as recited in claim 10, comprising anacceleration system for each said auxiliary electron source. 12.Apparatus as recited in claim 10, comprising a focusing device for eachauxiliary electron source, said focusing device producing linearfocusing of electrons from said auxiliary source.
 13. Apparatus asrecited in claim 1, comprising a glow discharge space in said ionizationdevice for ionization of said particles of impurities.
 14. Apparatus asrecited in claim 1, comprising a high-current arc discharge space insaid ionization device for ionization of said particles of impurities.15. Apparatus as recited in claim 14, comprising an auxiliary electrodeprovided with a small aperture, said high-current discharge spaceextending between the impact region of the working beam on the workpieceand said auxiliary electrode.
 16. Apparatus as recited in claim 10,wherein said auxiliary electron source is provided with an auxiliarycathode extending parallel to said working beam.
 17. Apparatus asrecited in claim 16, comprising a grid surrounding said auxiliarycathode and an envelope electrode surrounding said working beam and saidgrid.
 18. Apparatus as recited in claim 17 comprising a grid surroundingsaid electron source which is at a positive potential relative theretoand an envelope electrode surrounding said grid And at a negativepotential relative to said electron source, said potentials and thespacings of said grid causing electrons emitted by said electron sourceto be concentrated in the space between said grid and said envelopeelectrode and to execute oscillatory movement therein to producerelatively heavy negative and positive particles by ionization ofimpurities, said negative particles concentrating at said grid and saidpositive particles concentrating at said envelope electrode, saidparticles being at least in part, deposited on said grid and saidelectrode.
 19. Apparatus as recited in claim 9, wherein said ionizationdevice comprises an auxiliary electron source which produces electronsof lower energy than the electrons in said working beam, the apparatusfurther comprising at least two deflecting electrodes provided onopposite sides of said working beam said electrodes being charged todifferent electric potentials, said auxiliary electron source being sopositioned that auxiliary electrons generated thereby to produceionization are accelerated in the electric field between said deflectingelectrodes.
 20. Apparatus as recited in claim 9, wherein said ionizationdevice comprises an auxiliary electron source and a negative deflectingelectrode associated therewith, said electrode defining an aperture nearwhich said source is located.
 21. Apparatus as recited in claim 19,comprising a plurality of auxiliary electron sources and deflectingelectrodes arranged around part of the circumference of said workingbeam, said electrodes connected to substantially the same potential, andat least one relatively positive deflecting electrode occupying at leastpart of the remaining circumference.
 22. Apparatus as recited in claim10, wherein said auxiliary electron source is so formed that thelow-energy electrons therefrom move in the region of said working beamand substantially parallel thereto.
 23. Apparatus as recited in claim22, wherein said auxiliary electron source is provided with an auxiliarycathode at least partly surrounding the path of said working beam and anannular auxiliary anode offset with respect thereto along the directionof said working beam, said auxiliary anode accelerating the electronsemitted by said auxiliary cathode substantially parallel to said workingbeam.
 24. Apparatus as recited in claim 23, comprising at least onedeflecting device in an axial region of said working beam on the side ofsaid auxiliary electron source remote from said workpiece to beprocessed.
 25. Apparatus as recited in claim 23, comprising a focusingdevice for said auxiliary electron source, wherein said focusing deviceis so formed that it concentrates said electrons into a substantiallycylindrical space extending substantially coaxial to said working beam.26. Apparatus as recited in claim 10, comprising a magnetic device whichin the ionization region of said apparatus extends the tracks of saidelectrons supplied by said auxiliary electron device by curvaturethereof.
 27. Apparatus as recited in claim 26, comprising a working beammagnetic focusing device, wherein said auxiliary electron source is soarranged that said magnetic focusing device also acts to curve thetracks of electrons emitted by said ionization device.
 28. Apparatus asrecited in claim 1, wherein the acceleration path of the electrons insaid working beam lies outside of the working region of said deflectingdevice.
 29. Apparatus as recited in claim 1, wherein said screeningdevice is provided with at least one replaceable screen.